Panabaker on the spin-off pilot plays Caitlin Snow, a bioengineering expert who lost her fiancé during the particle accelerator snafu at Central City’s S.T.A.R. Labs. (The smart money has her one day evolving into Killer Frost.) Valdes meanwhile plays Cisco Ramon, S.T.A.R. Labs’ youngest genius (who may be fated to become the Justice Leaguer known as Vibe).

“The idea of bringing in those characters really, really appealed to us because it allowed us to honor our original intention [of] doing something Flash-related around Episode 19 or 20 without … basically paying Grant Gustin to sit around with his eyes closed/unconscious the whole episode,” Guggenheim explained, saying that Barry won’t emerge from his coma until The Flash (presumably) premieres this fall. “This episode is really cool. It allows us to further flesh out the Flash universe on Arrow.”